Electrophotographic process using organic photoconductors having at least two chromophores



United States Patent Int. Cl. G03g 5/00 US. Cl. 96--1 2 Claims ABSTRACTOF THE DISCLOSURE The organic photoconductors are certain linearmolecules having at least two chromophores such as a Schiffs base groupor an azo group joined to one another through a benzene ring or seriesof benzene rings. These compounds have been found to be useful asphotocondnctors in electrophotographic processes. Some of the compoundsare novel.

BACKGROUND OF THE INVENTION Field of the invention This inventionrelates to a class of organic photoconductive materials and, moreparticularly, relates to their use as photocondnctors inelectrophotographic processes, especially those utilizing contact reflexexposure.

Description of prior art A number of organic photocondnctors are knownin the prior art, but most of them have not achieved commercial successbecause their sensitivity or exposure speed is too slow to competefavorably with the commercially used inorganic photocondnctors, such asselenium. However, aside from speed, most organic photoconductors offermany advantages over the commercially used selenium. That is,photoconductive elements fabricated from organic photocondnctors areeasily manufactured, can be substantially translucent, and aresufficiently flexible to be used in belt configurations and theconfigurations of Us. patent application Ser. No. 649,162 filed June 22,1967, now abandoned.

US. patent application Ser. No. 668,697, filed Sept. 18, 1967, describesa contact reflex reproduction method. The compounds of the presentinvention are particularly useful in such a process.

US. patent applications Ser. No. 668,703, filed Sept. 18, 1967, now US.Pat. 3,489,558 and Ser. No. 668,696, filed Sept. 18, 1967, now US. Pat.3,501,293 both describe other compounds useful as organicphotoconductors.

SUMMARY OF THE INVENTION It has now been found that a class of compoundsoffer the advantages of organic photocondnctors, discussed above, and,in addition, exhibit dichroism. The compounds of the present inventionare those having the forwherein A is selected from the group consistingof X is selected from the group consisting of: CH==N), (N=CH) (N=N)(CH=CH-CH=N) and (N=CHCH=CH); and R is selected from the groupconsisting of hydrogen, nitro, lower dialkyl-amino, and lowerdialkyl-aminophenylazo.

Of the compounds covered by the above general formula, the mostpreferred ones are those in which R is lower dialkyl-aminophenylazowhile X is (CH=N-) and A is and also those in which R is lowerdialkyl-amino while X is (CH=CHCH=N-) and A is Both of these two classesof most preferred compounds are novel.

For the preparation of photoconductive elements, it is advantageous forthe compounds of the general formula to be dissolved in organicsolvents, such as tetrahydrofuran, or any other solvent in which thecompounds are at least partially soluble. Such solutions are applied tosubstrates suitable for electrophotography and the solvent is thenremoved. Mixtures of solvents can also be used.

Instead of the above preparation, the compounds of the general formulacan be used in conjunction with a resinous binder. Suitable resinsinclude both natural and synthetic resins, examples of which are balsamresins, phenol resins modified with colophony, coumarone resins, indeneresins, cellulose ethers, polyvinylchlorides, polyvinylacetate, acrylicpolymers, such as polymethyl acrylic esters, polystyrene,polyisobutylene, polyvinylnormal, polycondensates, such as phthalateresins, polyamides, and polyadducts, such as polyurethanes.

The proportion of resin to the photoconductive compound can varygreatly, but elements having a high proportion of resin and a lowproportion of photoconductive compound are the less desired. Mixtures ofat least equal parts resin and photoconductive compound are preferred.

The substrate material, if one is desired, may be any which satisfy therequirements of electrophotography such as metal, glass, paper, orplastic. Unless it is to be used in a device employing dual coronadischarge, such as US. Pat. 2,922,883, the substrate should preferablyhave a conductivity greater than 10- ohm cm.-

Application of the solutions of the compounds of the general class, withor without resins, is in the usual manner, such as 'by spraying, doctorblade, meniscus coating, etc., followed by drying.

One type of electrophotographic process in which the compounds of thepresent invention are useful is known as xerography. The processcomprises the laying down of the uniform electrostatic charge on aphotoconductive and insulating element, exposing the electrostaticcharge surinto contact with the developed image and transferred Ithereto and fixed thereon. The residual toner remaining on thephotoconductive insulating element is removed by cleaning and theelement is then ready for the preparation of the next copy or the nextcycle.

Because they have the additional advantage of being dichroic, thecompounds of the present invention are suitable for use in that type ofelectrophotography known as contact reflex reproduction, which is anelectrophotographic process for the production of related as a yellowcrystalline solid as shown in Beil., 14, 35. It had the followinganalysis.

Calcd. for C H N (percent): C, 77.8; H, 7.1; N, 15.1. Found (percent):C, 77.9; H, 7.1; N, 15.1.

EMMPLE II 1,4 bis benzylidene bis N,N dimethyl-p-phenylenediamine flexcopies in which a document is positioned adjacent a photoconductiveelement which exhibits photoconductive dichroism and has a preferredabsorption axis, and in which the photoconductive element is uniformlyexposed through the photoconductive element with polarized light whosevector, relative to the absorption axis, is such that the light is notabsorbed. The polarized light in striking the document is absorbed insome areas, nor- CHa and, hence, permits the formation of anelectrostatic charge pattern corresponding to the document.

The general nature of the invention having been set forth, the followingexamples are now presented as to the specific preparation of compoundsfalling within the above general class and the specific preparation ofthese compounds into photoconductive elements which are then used inelectrophotographic processes. The specific details presented are forpurposes of illustration and not limitation.

A general method for the preparation of the Schitfs base type ofcondensation product is as follows:

The difunctional aldehyde or diamine is dissolved in an alcohol such asn-butanol with a slight excess of the mono functional aldehyde or amineand heated to reflux for 6-2 hours. The resultant condensation productsprecipitate out of the hot reaction solvent and are hot filtered. Theyare subsequently washed with acetone, ether, 55

and dried.

Prepared according to the general procedure by refluxingterephthaldehyde and N,N-dimethyl-p-phenylenediamine in ethanol for onehour. Isolated as an orange solid.

Calcd. for C H N (percent): C, 77.8; H, 7.1; N, p

15.1. Found (percent): C, 78.3; H, 7.1; N, 14.5.

EXAMPLE III 4,4 bis(p-dimethylaminobenzylideneamino) stilbene Preparedfollowing the general procedure by reflexing 4,4 diaminostilbene and pdimethylaminobenzaldehyde for one hour in n-butanol. It was isolated asorange crystals as shown in Beil., 14 (I), 361.

Calcd. for C H N (percent): C, 81.3; H, 6.8; N, 11.8. Found (percent):C, 81.2; H, 6.8; N, 11.7.

EXAMPLE IV 4,4 bis(p-dimethylaminobenzylideneamino) bibenzyl Prepared bythe general procedure using n-butanol and refluxing 4,4' diaminobibenzyland p-dimethylaminobenz- 40 aldehyde for two hours. Isolated as yellowsolids,

Calcd. for C H N, (percent): C, 81.0; H, 7.2; N, 11.8. Found (percent):C, 81.1; H, 7.3; N, 11.7.

EXAMPLE V N,N bis(benzylidene) benzidine Prepared by the generalprocedure by refluxing benzidine 5 and benzaldehyde in ethanol for 1hour as referenced EXAMPLE VI N,N' bis (p-dimethylaminobenzylidene)benzidine EXAMPLE I N,N' bis(p-dimethylaminobenzylidene)p-phenylenediamine This compound was prepared by the above generalmethod by refluxing in ethanol for one hour. It was iso- 70 Prepared bythe general procedure by heating benzidine andp-dimethylaminobenzaldehyde in ethanol for one hour. Isolated as ayellow solid as shown in CA., 52:5197

Calcd. for C H N (percent): C, 80.7; H, 6.8; N, 12.5. Found (percent):C, 80.8; H, 6.9; N, 12.4.

EXAMPLE VII N,N' bis (9-julolidinidene) benzidine CHzCHzCHz CHaCHz (EH3Prepared by the general procedure refluxing 9-formyl- '1 g. 4,4diaminostilbene and 3 g. p-N,N-dimethylaminojulolidene and benzidine inn-butanol for two hours. Isocinnamaldehyde in 150 ml. n-butanol wererefluxed for lated as yellow solids. 45 minutes. The resultingprecipitate was hot filtered and Calcd. for C H N (percent): C, 82.8; H,6.9; N, washed with acetone, ether and dried. Recovered 0.75 g.

10.2. Found (percent): C, 82.7; H, 6.9; N, 10.3. brown solids. Theproduct had the following analysis.

This compound fits into the general formula given 5 Calcd. for C H N(percent): C, 82.4; H, 6.9; N, above when the lower dialkyl-amino groupR is consid- 107. Found (percent): C, 81.6; H, 6.8; N, 10.9.

ered to be linked at both ends to the phenyl ring. d 'g q Bowl Compoundwas found to be y highly 1 or EXAMPLE VH1 c 0 EXAMPLE XIV N,N' bis(p-dimethylaminophenylazobenzilidine) A photoconductive element wasprepared by dispersing benzidine N,N bis(p dimethylaminobenzylidene)pphenylenedi- CH; CH:

01 13 cHa Prepared by the general procedure by refluxing benzidine amine(the compound prepared in Example I above) in andp-dimethylaminophenylazobenzaldehyde in ethanol an equal weight ofpolystyrene dissolved in 1,2-dichlorofor A hour. Isolated as redcrystals. ethane and coating the solution on an aluminum slide Calcd.for C H N (percent): C, 77.0; H, 5.8; N, with a doctor blade set at a 5mil wet gap. The thus 17.1.Found (percent): C, 76.1; H, 5.9; N, 16.9.prepared photoconductive element was uniformly elec- This novel compoundwas found to be dichroic to an trostatically charged using a Xerox ModelD Processor at outstanding degree. a potential of +7000 volts. Aftercharging, the element EXAMPLE IX was exposed to a 375 watt GE Photo EBRlamp at a distance of 12 inches for 2 seconds and using positive trans-(p-dimethylaminocinflamalidene) benzidine parency as a document to becopied. The formed elec- Prepared y the general Procedure y refluxingbfinzidine trostatic image was developed with negatively charged andP-dimetPY1amininnama1dehde in ethanol for toner (Xerox 914) across thephotoconductive element. hour. It was lsolated as a brown sohd.

Calcd. for C34H34N4 (percent): C, 80.2; H 69; N Again using the XeroxModel D Processor, the toner 11.2. Found (percent): C, 80.3; H, 6.9; N,11.6. 35 image Was transferred to p p y spraying positive EXAMPLE Xcharges on the back of the paper. After transfer of the 4,4-bis(p-dimethylaminophenylazo) biphenyl toner image, the toner was fused tothe paper on a hot CH: CE; a This was prepared by diazotizing benzidineand coupling plate to yield a high quality copy of the document withwith dimethyl amiline as outlined in Aust. J. Chem., 1455 high contrast,high image density, and faint background.

(1967). EXAMPLE XV EXAMPLE XI A photoconductive element was prepared bydispers- 4,4 (bis p-nitrocinnamylidene) benzidine ing N,N'bis(p-dimethylaminophenylazobenzilidine)ben- 0.45 g. benzidine and 1.5g. p-nitrocinnamaldehyde in zidine (the compound of Example VIII above)in an 100 ml. n-butanol were refluxed for 1 hour. The resultequal weightof polystyrene dissolved in 1,2-dichloroething precipitate was hotfiltered and washed with acetone, ane and coating the solution on analuminum slide with ether and dried. Recovered 1.05 g. red coloredsolids. a doctor blade set at a 5 mil Wet gap. The thus prepared Calcd.for C H N O (percent): C, 71.7; H, 4.4; N, photoconductive element wasuniformly electrostatically 11.2. Found (percent): C, 71.8; H, 4.5; N,11.4. charged using a Xerox Model D Processor at a potential EXAMPLE XIIof +7000 volts. After charging, the element was exposed to a 375 watt GEPhoto EBR lamp at a distance of 12 inches for 0.1 second and usingpositive transparency Bis (p-dimethylaminophenylimino) bis1,4-phenylene-2- propeneylidene as a document to be copied. The formedelectrostatic H3O CH3 N N=HC-HC=HC -CH=CH-CH=N N 1130 CHa Bis1,4-phenylenepropenal and N,N-dimethyl-p-phenylimage was developed withnegatively charged toner f i are refluxed 1I1 ethanol- The resultant P(Xerox 914) across the photoconductive element. Again ciprtate is hotfiltered and the product worked up 1n a using the Xerox Model DPrecassor the toner image manner analogous to the above examples wastransferred to paper by spraying positive charges EXAMPLE XIII on theback of the paper. After transfer of the toner 4,4 -bis(p-dimethylaminocinnamylideneamino) stilbene image, the toner was fusedto the paper on a hot plate CH3 CH3 CH3 CH3 7 to yield a high qualitycopy of the document with high contrast, high image density, and faintbackground.

EXAMPLE XVI 10% polyvinyl carbazole in benzene 40 Benzene a 20Chloroform 30 Toluene 10 1,3-dinitronaphthalene 0.04

1% benzene solution of a plasticizer consisting of a combination ofpolymers of esters of acrylic acid and methacrylic acid 8 Thisformulation is coated at 3 feet per minute on a meniscus coater andcured for 1 hour at 90 C. Electrometer results show a charge acceptanceof about 600 v. The film is used to make robot copies in the contactreflex mode. 7

While the invention has been shown and described with reference topreferred embodiments thereof, it will be appreciated by those skilledin the art that variations in form may be made therein without departingfrom the spirit and scope of the invention.

What is claimed is:

1. In an electrophotographic reproduction process which comprisesselectively rendering portions of a photoconductor electricallyconductive by selective exposure to light, the improvement according towhich the photoconductive element comprises a compound selected from thegroup consisting of compounds having the formula:

wherein A is selected from the group consisting of CH2CH2 X is selectedfrom the group consisting of:

-cH=N-) (-N= H) N=N) (CH =CHCH=N) and (N=CH-CH=CH-); and R is selectedfrom the group consisting of hydrogen, nitro, lower dialkylamino, andlower dialkyl-aminophenylazo.

2. A step of exposing the photoconductive element as claimed in claim 1wherein the process is carried out in the contact reflex mode.

References Cited UNITED STATES PATENTS 3,066,023 11/1962 Schlesinger96-1 3,163,532 12/1964 Schlesinger 96-1 3,335,003 8/1967 Snelling 96-13,489,558 1/1970 Clecak 96-1 GEORGE F. LESMES, Primary Examiner M. B.W'ITTENBERG, Assistant Examiner U.S. Cl. X.'R.

